Kirkwall

(Spoilers abound here for Dragon Age II, and the Legacy DLC, possibly for Inquisition, although I am focusing on Kirkwall, so maybe not)

From the start, Kirkwall is painted as a terrible place to be. The mages are housed in a slave prison, and it doesn't seem to be any less dismal. The guard are somewhat corrupt, demanding bribes to enter the city, even from those with a legitimate claim to be there. When the Hawkes get into the city proper, it's not much better, while they are fairly lucky: having someone get them into the city; a roof over their heads; food to eat; and a job - yes, it's indentured servitude, but clearly Hawke made a name for him/herself in Kirkwall, got a reputation as someone who gets things done. Without the servitude, they'd have been just another destitute Fereldan begging on the streets, like so many of their countrymen.

Then we get to the meat of the story, and a chance to delve into Kirkwall's Tevinter history, through the Enigma of Kirkwall codex entries. The streets themselves are in the shape of blood magic sigils. Roughly one tenth of the slaves that arrived in Emeritus (as it was called, back then) vanished. The Veil is in tatters. the ratio of blood mage and/or possessed to not, is far closer than elsewhere in Thedas (other than Tevinter itself). Demons can and do possess non-mages, and if the Exiled Prince DLC is anything to go by, they will aid non-mages in using blood magic. (the Harimann family)

Then we come to the Legacy DLC. This shows a few other disquieting details about Kirkwall. There is an ancient Darkspawn Magister in the nearby Vimmark Mountains. One that can influence - even while he is sealed and asleep - any tainted being. When he first wakes his words seem to imply that he entered the black city ("The City. It was supposed to be golden. It was supposed to be ours") If taken at face value, (which, given his disorientation when he woke, is a fair assumption) this suggests that he was one of the seven Magisters Sidereal. (Information found in Dragon Age: Inquisition removes all doubt, of course) It also seems that from his perspective, this event had only recently occurred.

There is a series of codices (Amgeforn) that refer to another being - Malvernis - apparently even older and more powerful than Corypheus, sealed just outside the Grey Warden prison.

Put all these facts together - and I am sure that there is more that I have missed at the moment - and a terrifying conclusion can be drawn:

Kirkwall/Emeritus is undoubtedly the location of the attempt by the Magisters Sidereal to enter the Fade. Corypheus being so close to the city. The clear use of blood magic, most likely from the blood of the 1/10 of the slaves that vanished when they reached the city. The corrupting entity sealed in the mountains by the Dwarves. The shredded veil, and the ever present demons. It all adds up to Kirkwall being corrupted beyond recovery. Were I in a position to do so, I would recommend that the city be razed, the smallest stones crushed to dust, and the whole area cleansed with fire, so no-one could live there.

(All codex entries referenced here can be found on the Dragon Age Wikia, indeed, that is where I fact-checked)